The present invention relates to a method of monitoring microbe in water, and more particularly, it relates to a monitoring method which is suitable for monitoring an existence or a propagation condition of pathogenic microbe, such as Cryptosporidium, in a water purifying plant.
In recent years, there have been reported examples of group infections to Cryptosporidium in Japan (xe2x80x9cMizujohoxe2x80x9d 16(3), PP. 8-11, 1996), and in this report, over sixty percent of seven hundred and several tens of people exposed to protozoa was infected. It is considered that this example was caused due to a contamination of a water receiving vessel in a building, but in Illinois in U.S.A., a large-scaled water-related group infection occurred in 1993 such that 1.6 million people were exposed and 0.4 million people were infected.
According to the above report, Cryptosporidium is a parasitic protozoan (protozoa), and one, which infects healthy person to cause a diarrhea, is a small C. parvum which parasitizes in a small intestine. A large C. muris, which parasitizes in a stomach of other animals, has been also known. It has been known that C. parvum causing a water-related group infection has no specific host, and infects a large range of mammals. Also, Cryptosporidium exists outside the host as an oocyst, and inside the oocyst, there is contained a polypide (sporozoites) which is a main body of the infection to the host. In oocyst, which is an existence configuration of C. parvum in question has an ellipsoidal shape close to a sphere having a size (particle diameter) of about 5 xcexcm. Since C. parvum is covered by an oocyst wall to protect an inside, it has a strong resistance against a decontaminating chemical or disinfectant, so that it has an extremely high resistance against chlorine used in a water purifying plant. Thus, C. parvum has a characteristic that it is difficult to be inactivated by decontamination or sterilization in the water purifying plant.
From the foregoing, even though an example of a massive infection has not been reported at this moment in Japan, there is a very high possibility that when Cryptosporidium exists or is propagated in a raw water reservoir or a clear water reservoir, it is taken into a large number of people to cause infection through a water supply. Thus, it is strongly desired to monitor an existence or propagation condition of Cryptosporidium, but an only method of monitoring Cryptosporidium available now is a method of monitoring a turbidity of water. In this method, although an existence of Cryptosporidium can be recognized in detail by an already-established analytical method, such as fluorescent antibody method, this type of analytical method is very cumbersome, so that it is not realistic to use this method as a regular monitoring method in a water purifying plant or the like. Thus, this method has not been actually used.
Incidentally, in order to strengthen a system of monitoring Cryptosporidium relying only on monitoring the turbidity of water, adopting a fine particulate counter has been considered, but it is difficult to monitor the existence or the propagation condition of Cryptosporidium by this method. Namely, although a monitored object is a pathogenic microbe called xe2x80x9cCryptosporidiumxe2x80x9d, there is an unspecified number of materials in water of the raw water reservoir or the water purifying reservoir, so that all of them are subjected to be measured. Since the fine particulate counter requires a calibration using a specific material, it is difficult to measure all of the particles in water in the water purifying plant wherein the unspecified number of materials exists, accurately. Thus, it is actually impossible to presume or determine an existence or absence of Cryptosporidium.
The present invention has been made in view of the foregoing, and an object of the invention is to provide a method of monitoring microbe in water, wherein water in, such as a raw water reservoir or a water purifying reservoir in the water purifying plant, containing particles of an unspecified number of materials, is the subject to be examined, and information relating to a propagation condition, and an existence or absence of the specific microbe, such as Cryptosporidium, in water can be obtained.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To achieve the above object, a method of monitoring microbe in water according to the present invention is a method of monitoring an existence or a propagation condition of the specific microbe having a known particle diameter in water, wherein a particle size analyzer on the laser diffraction having a flow cell through which a fluid can flow is used, and object water or liquid to be monitored is guided to an inside of the flow cell continuously or intermittently, to thereby measure a spatial intensity distribution of the diffracted and scattered light obtained by irradiating the laser beam in the flow cell in the condition that the monitored object water flows inside the flow cell. Then, the particle size distribution of the particles existing in the monitored object water is calculated from the measured result, and from the calculated result of the particle size distribution and the substantial particle diameter of the specific microbe which should be monitored, the existence or the propagation condition of the microbe is determined.
In the present invention, by using the particle size analyzer based on the laser diffraction method, a particle size distribution of the particles formed of the unspecified number of materials existing in water is accurately measured, to thereby assume or determine a possibility of an existence of the specific microbe which has a known particle diameter.
Namely, the particle size analyzer base on the laser diffraction method generally measures a spatial intensity distribution of a diffracted and scattered light obtained by irradiating a laser beam to a group of particles which are in a dispersed and flying condition in a medium, and by utilizing a fact that the light intensity distribution follows or relies on the Mie""s scattering theory and Frauhhofer""s diffraction theory, the particle size distribution of the group of the particles is obtained from the measured result of the spatial intensity distribution of the diffraction and scattering light by the computation based on the Mie""s scattering theory and Fraunhofer""s diffraction theory. In applying to the present invention, a group of the measured particles is a group of particles formed of various kinds of materials contained in the monitored object water, and the medium is water, so that a measurement is a wet measurement. Namely, the spatial intensity distribution of the diffraction and scattered light, which is obtained by irradiating the laser beam to the flow cell in the condition that the monitored object water flows inside the flow cell, is measured. In this measurement, it is only required that the monitored object water is made to flow in the flow cell continuously, or the monitored object water is made to flow intermittently with a predetermined interval, and the laser beam is irradiated at an adequate timing.
In this particle size analyzer based on the laser diffraction method, if refractive indices of the medium and the measured particle are known, an accurate particle size distribution can be obtained from the measurement result of the spatial intensity distribution of the diffraction and the scattered light. In applying to the present invention, the medium is water, and the refractive index thereof is known. Thus, as to the specific microbe, in case a substantial particle diameter of the microbe is known, even if the refractive index is unknown, a spatial intensity distribution of the diffracted and scattered light of a group of the measured particles formed of the microbe is measured in advance. Then, by setting the refractive index of the group of the measured particles such that the conversion result to the particle size distribution coincides with the known substantial particle diameter of the microbe, the useful refractive index thereof can be presumed.
Accordingly, while the presumed result in regard to the specific microbe is set as the refractive index of the group of the measured particles, the refractive index of water is set as the refractive index of the medium. Then, when a spatial intensity distribution of the diffracted and scattered light by the group of the particles in the monitored object water is converted into the particle size distribution, at least as to the specific microbe, the particle diameter is accurately obtained to reflect in the computed result of the particle size distribution naturally. Thus, if there is a microbe which should be monitored in the monitored to object water, the distribution corresponding to the particle diameter of the microbe should exist in the measured result of the particle size distribution.
Here, in case the existence of the particle corresponding to the particle diameter of the specific microbe is recognized in the group of the particles in the monitored object water, the particle is not always a specific microbe. However, it can be used at least as an index showing a possibility of the existence, and in this case, for example, an alarm may be issued to encourage an operation of the known and detail analysis, such as the fluorescent antibody method.